1. Field of the Invention
The invention relates to detecting, distinguishing and counting objects in an operating room using a detection device which responds to an alternating electromagnetic field.
2. Description of the Prior Art
Despite precautions, surgeons still occasionally leave surgical objects such as sponges and, less frequently, small surgical tools in their patients after an operation. Areas which are badly injured tend to have a great amount of blood which may cover the surgical objects, making the objects hard to locate. Also, objects may find their way under an organ. This is most likely to occur in surgical areas such as the abdomen which is large and has many organs.
The prior art discloses use of X-ray opaque material positioned on the surgical devices in order that after the surgery is completed and the wound is closed, an X-ray can be taken to insure that no surgical objects were left within the patient. Although this detection method is effective, it is cumbersome. Most operating rooms do not have X-ray machines. Hence, the patient must be taken to another room. There the patient often must be moved from his gurney to an X-ray table for X-rays to be taken. If a surgical object is detected after an X-ray has been taken, the patient must be returned to the operating room. Then, the cavity or incision must be reopened to remove the surgical object and then reclosed. This second surgery can cause a great deal of trauma to the patient, preventing optimum healing. Examples of surgical sponges which are marked by radiopaque material are disclosed in U.S. Pat. No. 2,190,432 to Lewison, U.S. Pat. No. 2,698,270 to Mesek, U.S. Pat. No. 4,185,626 to Jones et al., and U.S. Pat. No. 4,205,680 to Marshall.
Manual counting of the sponges and other surgical objects after the surgery is completed is also used to prevent those objects from being left in body cavities. This is not a foolproof method. Fatigue, poor handwriting, and misreading of numbers will occur during operations lasting 4 to 12 hours when dealing with badly damaged patients. Consequently, miscounts occur as a result of human error.
Surgical objects are counted not only to insure that no such objects are left in the human body, but also to prevent such objects from being inadvertently discarded. There have been instances where a surgical item costing several thousand dollars has been discarded with the surgical trash.
Presently, many operating rooms follow a practice of placing all used and soiled sponges, drains, packs and other objects in a holding container. At the end of the operation the container is emptied and the objects that had been contained therein are counted. Blood on the discarded objects may contain infectious disease viruses. Therefore, each time a soiled surgical object is handled there is a risk of accidental self inoculation. Consequently it is desirable to minimize the handling of such objects, not handle each discarded object twice as in this current practice.
Because of the risks of infection and in an effort to minimize human error, the art has developed several methods of marking objects for automatic detection. Many of those methods rely upon markers which respond to a magnetic or electromagnetic field.
Greenberg in U.S. Pat. No. 3,587,583 attempts to overcome the problems of leaving surgical objects within the human body. He proposes to mark the surgical object with a permanently magnetized material. A surgeon performs an operation in the normal manner. Before closing the incision the surgeon probes for the presence of a surgical object with a magnetic field detector means which generates an electric signal which is modified in the presence of a magnetic field. If the marked object is present, the magnetic field of the magnetic marker is sensed by the magnetic field detector means, which modifies the electric signal. Yet, an operating room has many types of equipment which generate permanent magnetic fields. The presence of those fields can activate the magnetic field detector means, giving false detection. Because of its unreliability in an operating room, Greenberg's device is not a practical solution to the problem.
In U.S. Pat. No. 5,057,095, Fabian proposes to mark surgical instruments with a marker adapted to produce identifying signal characteristics when exposed to an alternating magnetic field. He discloses three types of resonant markers that are able to resonate at a certain preselected frequency. The first marker is a magnetomechanical device comprised of a permanent magnet overlaying a magnetostrictive metal strip in a plastic housing. The magnetostrictive strip vibrates when the marker is exposed to an alternating electromagnetic field, and its resonance is detected when the frequency of the applied field reaches a predetermined value. However, such devices are very sensitive to pressure and stress, which will inhibit them. Since a body cavity is under some pressure and the marker may be stressed during surgery, this type of marker is not reliable for use as a marker for surgical objects. The second proposed type is an electromechanical circuit comprised of an air coil, with or without a ferrite core, and a resonant structure such as a piezoelectric crystal. As the first type, this type of marker can be adversely affected by pressure and stress because its principle of detection relies on a electro-mechanical resonance; therefore, a piezoelectric crystal type marker is also unsatisfactory. The third type of marker proposed by Fabian is an electromagnetic LCR circuit. This type of marker can be either built out of discreet components or made of a flexible printed circuit. In the former case, this unit is expensive to build and bulky, and it is impractical for surgical sponges. In the latter case, due to its high electrical resonance frequency this type of marker can be adversely affected by the presence of metal objects and conductive media. Because the human body is conductive, this type of marker is also impractical for surgical sponges. Consequently, none of the markers proposed by Fabian, nor the Greenberg marker, has been available on the market.
In U.S. Pat. No. 5,045,071, McCormick teaches about the use of magnetic materials for accurately locating the position of a catheter which has been inserted into a blood vessel. At column 9, lines 12-16, the patent cross references U.S. Pat. Nos. 4,416,289, 4,431,005 and 4,445,501 for an explanation of the general method of detection. At column 5, lines 41-52, the '005 patent explains that a distortion of the magnetic field indicates the presence of the catheter. Thus, the McCormick patent teaches that merely a change in the magnetic field is a sufficient indicator of the position of the marked object. However, McCormick's measurements can be affected by the presence of other nearby magnetic and conductive materials. Hence, McCormick's technique can and likely will provide "false positives" as to the presence or the position of the marked object.
Thus, there is a need for a marking method and apparatus for detecting and counting surgical objects within the human body and elsewhere in an operating theater utilizing a material that can be readily identified before the patient leaves the operating suite. The method and marker must not give false positives or otherwise be ineffective in the presence of magnetic and electromagnetic fields of the type commonly produced in the operating room. Such a marker and method may also be useful outside the operating room in environments where objects must be counted or detected and in which magnetic or electromagnetic fields are present.